@@ -1363,18 +1363,6 @@ void blk_account_io_start(struct request *rq, bool new_io)
part_stat_inc(part, merges[rw]);
} else {
part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq));
- if (!hd_struct_try_get(part)) {
- /*
- * The partition is already being removed,
- * the request will be accounted on the disk only
- *
- * We take a reference on disk->part0 although that
- * partition will never be deleted, so we can treat
- * it as any other partition.
- */
- part = &rq->rq_disk->part0;
- hd_struct_get(part);
- }
part_inc_in_flight(rq->q, part, rw);
rq->part = part;
}
@@ -344,11 +344,12 @@ static inline int sector_in_part(struct hd_struct *part, sector_t sector)
* primarily used for stats accounting.
*
* CONTEXT:
- * RCU read locked. The returned partition pointer is valid only
- * while preemption is disabled.
+ * RCU read locked. The returned partition pointer is always valid
+ * because its refcount is grabbed.
*
* RETURNS:
* Found partition on success, part0 is returned if no partition matches
+ * or the matched partition is being deleted.
*/
struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
{
@@ -359,17 +360,25 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
ptbl = rcu_dereference(disk->part_tbl);
part = rcu_dereference(ptbl->last_lookup);
- if (part && sector_in_part(part, sector))
+ if (part && sector_in_part(part, sector) && hd_struct_try_get(part))
return part;
for (i = 1; i < ptbl->len; i++) {
part = rcu_dereference(ptbl->part[i]);
if (part && sector_in_part(part, sector)) {
+ /*
+ * only live partition can be cached for lookup,
+ * so use-after-free on cached & deleting partition
+ * can be avoided
+ */
+ if (!hd_struct_try_get(part))
+ break;
rcu_assign_pointer(ptbl->last_lookup, part);
return part;
}
}
+ hd_struct_get(&disk->part0);
return &disk->part0;
}
@@ -288,6 +288,12 @@ static void hd_struct_free_work(struct work_struct *work)
static void hd_struct_free(struct percpu_ref *ref)
{
struct hd_struct *part = container_of(ref, struct hd_struct, ref);
+ struct gendisk *disk = part_to_disk(part);
+ struct disk_part_tbl *ptbl =
+ rcu_dereference_protected(disk->part_tbl, 1);
+
+ rcu_assign_pointer(ptbl->last_lookup, NULL);
+ put_device(disk_to_dev(disk));
INIT_RCU_WORK(&part->rcu_work, hd_struct_free_work);
queue_rcu_work(system_wq, &part->rcu_work);
@@ -309,8 +315,12 @@ void delete_partition(struct gendisk *disk, struct hd_struct *part)
struct disk_part_tbl *ptbl =
rcu_dereference_protected(disk->part_tbl, 1);
+ /*
+ * ->part_tbl is referenced in this part's release handler, so
+ * we have to hold the disk device
+ */
+ get_device(disk_to_dev(part_to_disk(part)));
rcu_assign_pointer(ptbl->part[part->partno], NULL);
- rcu_assign_pointer(ptbl->last_lookup, NULL);
kobject_put(part->holder_dir);
device_del(part_to_dev(part));
delete_partition() clears the cached last_lookup partition. However the .last_lookup cache may be overwritten by one IO path after it is cleared from delete_partition(). Then another IO path may use the cached deleting partition after hd_struct_free() is called, then use-after-free is triggered on the cached partition. Fixes the issue by the following approach: 1) always get the partition's refcount via hd_struct_try_get() before setting .last_lookup 2) move clearing .last_lookup from delete_partition() to hd_struct_free() which is the release handle of the partition's percpu-refcount, so that no IO path can cache deleteing partition via .last_lookup. It is one candidate approach of Yufen's patch[1] which adds overhead in fast path by indirect lookup which may introduce one extra cacheline in IO path. Also this patch relies on percpu-refcount's protection, and it is easier to understand and verify. [1] https://lore.kernel.org/linux-block/20200109013551.GB9655@ming.t460p/T/#t Reported-by: Yufen Yu <yuyufen@huawei.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: Hou Tao <houtao1@huawei.com> Signed-off-by: Ming Lei <ming.lei@redhat.com> --- block/blk-core.c | 12 ------------ block/genhd.c | 15 ++++++++++++--- block/partitions/core.c | 12 +++++++++++- 3 files changed, 23 insertions(+), 16 deletions(-)